The present invention relates to vacuum drum washers and, more particularly, to a vacuum drum washer used for washing pulp in a paper making process.
The assignee of the present invention currently supplies two styles of drums—the so-called BMax (shown in FIGS. 1 and 2) and the so-called VMax (shown in FIG. 3). The BMax is commonly referred to as an “end-draining” drum since all of the filtrate moves to the end (lengthwise) of the drum through annular channels located beneath the deck. In the BMax, the filtrate is then transferred to the valve area of the drum via radial channels built into the head of the drum.
The VMax is commonly referred to as a “center-draining” drum since all of the filtrate moves to the middle (lengthwise) of the drum through annular channels located beneath the deck. In the VMax, the filtrate is then transferred to the valve area of the drum via pipes (see FIG. 3).
The annular channels (shown in FIGS. 1 and 3) beneath the deck in both the BMax and VMax are referred to as filtrate channels.
End-draining drums are typically used for drums that are ≦20′ in length (sometimes longer, depending on the application). Center-draining drums are typically used for drums>20′ in length. The length criteria is based on limiting the distance filtrate has to travel when the volume is high, thereby reducing the pressure drop. Up until the early 1990's, most drums were of the center-draining design. The end-draining type drum was designed to lower the cost, and to simplify the drum construction for better maintainability.
An example of an existing drum is described in U.S. Pat. No. 5,021,126, the contents of which are hereby incorporated by reference.
A problem with the existing designs, however, is that the center-draining drum is costly, which has been amplified by the rising cost of steel.